The tangent and cotangent are reciprocals, as they should be. You can draw a right triangle with side opposite X having length 3 and the side adjacent to X having length $\displaystyle\sqrt{{7}}\usepackage{cmbright}\Huge\$ . Using the Pythagorean Theorem, you will find that the hypotenuse is 4. It follows that: $\displaystyle{\sin{{X}}}=\frac{{o}}{{h}}=\frac{{3}}{{4}}\usepackage{cmbright}\Huge\$